U.S. Pat. No. 4,037,082 to a Positive Temperature Coefficient Semiconductor Heating Device invented by Tamada et al. discloses an arrangement of components for constructing a heating device employing a plurality of positive temperature coefficient semiconductor (PTCS) heating elements as a PTCS heating element, upper and lower insulating plates, a heat emission plate and a case for entirely covering the layers of the PTCS heating element and the upper and lower insulating plates.
However, such a conventional PTC heating device still has the following drawbacks:
1. The PTC heating element sandwiched between the upper insulating plate and the lower insulating plate is encased in between a case and a heat emission plate by fixing screws or rivets through several holes punched in all side edges formed in the case and the emission plate. Whenever the device is operated at a raised temperature, the heat may cause thermal expansion of some elements which are not stably secured with one another to form gap between some electrical or thermal contecting elements, thereby impairing their electrical heating efficiency or shortening their service life.
2. Two metal film electrodes are provided in each PTC heating element, each electrode having a plurality of strips with fork-like configuration which are separated with each other by a predetermined distance T. So, the two opposite electrodes must be precisely made to prevent a short circuit caused therebetween. Any unexpected false connection or short-circuit of the two electrodes may cause electric sparking hazard or fire accident and may lose the heating effect by such a "complex" fork-like electrodes.
3. From the drawings illustrated in Tamada's patent, their terminals are protruded upwardly from the case and each PTC element is held in a square or rectangular socket formed in the case so that it is difficult to arrange a plurality of PTC elements longitudinally in the case. Such a conventional heating device can be modified inferentially to form a plurality of cases in that each case should then be respectively secured on a longitudinal continuous base plate by rivets or screws to increase its installation complexity and cost.
The present inventor has found the drawbacks of such a conventional PTC heating device, and invented the present fully clad PTC heating means.